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Each antibody binds to a specific antigen in a highly specific interaction analogous to a lock and key.. An antibody (Ab) or immunoglobulin (Ig) is a large, Y-shaped protein belonging to the immunoglobulin superfamily which is used by the immune system to identify and neutralize antigens such as bacteria and viruses, including those that cause disease.
An antibody digested by papain yields three fragments, two Fab fragments and one Fc fragment An antibody digested by pepsin yields two fragments: a F(ab') 2 fragment and a pFc' fragment The fragment crystallizable region ( Fc region ) is the tail region of an antibody that interacts with cell surface receptors called Fc receptors and some ...
Each immunoglobulin class differs in its biological properties and has evolved to deal with different antigens. [5] Antibodies are synthesized and secreted by plasma cells that are derived from the B cells of the immune system. An antibody is used by the acquired immune system to identify and neutralize foreign objects like bacteria and viruses.
Some antibodies form polymers that bind to multiple antigen molecules.. Immunoglobulin D (IgD) is an antibody isotype that makes up about 1% of proteins in the plasma membranes of immature B-lymphocytes where it is usually co-expressed with another cell surface antibody called IgM.
The IgG, IgE and IgA antibody isotypes are generated following class-switching during germinal centre reaction and provide different effector functions in response to specific antigens. IgG is the most abundant antibody class in the serum and it is divided into 4 subclasses based on differences in the structure of the constant region genes and ...
The Fc receptors bind the antibodies at their Fc region (or tail), an interaction that activates the cell that possesses the Fc receptor. [23] Activation of phagocytes is the most common function attributed to Fc receptors.
IgM antibodies do not pass across the human placenta (only isotype IgG). [48] These two biological properties of IgM make it useful in the diagnosis of infectious diseases. Demonstrating IgM antibodies in a patient's serum indicates recent infection, or in a neonate's serum indicates intrauterine infection (e.g. congenital rubella syndrome).
The "upper" part of an antibody. The complementarity-determining regions of the heavy chain are shown in red (Complementarity-determining regions (CDRs) are polypeptide segments of the variable chains in immunoglobulins (antibodies) and T cell receptors, generated by B-cells and T-cells respectively. CDRs are where these molecules bind to their ...